Typical memory disks comprise a substrate plated with a hard material such as a nickel phosphorus alloy. The nickel phosphorus is then "textured" (i.e., roughened). An underlayer, a magnetic alloy or magneto-optical material, and a protective overcoat are then deposited on the nickel phosphorus, e.g., by sputtering. The memory disk manufacturing process leaves the surface of the disk in a slightly roughened condition often with asperities, voids, or contamination.
A memory disk, such as the type used in a computer hard disk drive, is generally mounted on a spindle driven by a motor to rotate the disk at high speed. A read/write head, kept in close proximity to the surface of the rotating disk, reads or writes data on the disk. The read/write head is separated from the disk surface by an air bearing created by the high speed rotation of the disk. The read/write head flies on this air bearing, e.g., at a height of approximately one microinch, although this height is getting lower with advancing technology. The closer the read/write head is to the disk surface, the more information that may be written on the disk. Thus, it is desirable for the read/write head to fly as close as possible to the disk.
The precision with which the read/write head flies over the memory disk requires that care is taken during manufacturing of the disk to assure that there are no asperities or contamination on the surface of the disk that are large enough to interfere with the read/write head. If a defect on the disk surface contacts the read/write head during use, the read/write head or the disk may be damaged. To prevent undesired contact between the read/write head and the disk, it is important to remove from the disk surface any defects that are large enough to interfere with the read/write head.
A "burnishing head" is used in magnetic disk or magneto-optical disk manufacturing to remove asperities or contamination from the disk surface that may interfere with the read/write head. An example of a burnishing head is described in U.S. Pat. No. 4,845,816.
Burnishing heads use rhomboid or diamond shaped pads. FIG. 1 shows an enlarged view of the bottom surface of a burnishing head 2 with a plurality of burnishing pads 4. Each burnishing pad 4 is diamond shaped and has sharp edges 6 and 8. Edges 6 and 8 contact and cut protrusions on the memory disk surface as the disk rotates beneath burnishing head 2. Burnishing head 2 also has a tapered leading edge 10. FIG. 2A illustrates burnishing head 2 attached to a suspension arm 13 over the surface of a disk 14, which is rotating in the direction of arrow 16. The high speed rotation of disk 14 creates an air cushion or bearing over the surface of disk 14. Lift is created under burnishing head 2 when the air bearing contacts tapered leading edge 10 and the large air bearing surface area, which is formed by the bottom of pads 4.
As shown in FIG. 2A, burnishing head 2 flies over the surface of disk 14 at a slope angle .theta., approximately 0.015 degrees. Because burnishing head 2 flies at angle .theta., any contact between burnishing head 2 and the surface of disk 14 is primarily at the trailing edge 18. Thus, trailing edge 18 wears down more quickly then the rest of burnishing head 2. As shown in FIG. 2A, the trailing edge 18 is a distance d.sub.d1 above disk 14 and the leading edge 10 is a distance d.sub.d2 above disk 14, where d.sub.d1 is less than d.sub.d2 because burnishing head is at an angle .theta.. FIG. 2B shows a burnishing head 3 that has been worn with use. As shown in FIG. 2B, worn burnishing head 3 flies at the same angle .theta.. The leading edge 10 of burnishing head 3 is a distance d.sub.d4 from disk 14, which is the same height as distance d.sub.d2 as shown in FIG. 2A. However, the trailing edge 18 of worn burnishing head 3 has been worn away. Thus, distance d.sub.d3 of trailing edge 18 in FIG. 2B is greater than distance d.sub.d1 in FIG. 2A. Accordingly, worn burnishing head 3 is less effective than burnishing head 2.
Also, burnishing head 2 sometimes rolls as it flies over the surface of disk 14. Any roll of burnishing head 2 will cause a corner on trailing end 18 to contact the surface of disk 14, which may result in scratching, gouging or other damage to disk 14.
Burnishing head 2 has channels 12, which separate diamond pads 4 from each other. Channels 12 are intended to accept debris as protrusions are cut from the surface of disk 14. However, debris tends to accumulate in channels 12. With the accumulation of debris in channels 12, debris contamination may be spread to other parts of the memory disk, as well as to other memory disks upon which the burnishing head is subsequently used. The accumulated debris may gouge or otherwise damage areas of the memory disk which the debris contacts. Debris accumulation is caused by the straight sides of channels 12 disrupting and reflecting air flow through channels 12 during use of burnishing head 2. Also, there is generally some residue remaining from the burnishing head manufacturing process in channels 12. Due to the small size of channels 12, typically 0.0045 inches across, it is difficult to clean channels 12 of all manufacturing residue. Thus, once debris from the cut protrusions is swept into the channels 12, the debris tends to accumulate within the channels due to the residue already present in channels 12 and the lack of air flow through channels 12.
FIG. 3A is a graph showing the performance of an unused 70%, 4.5 mil diamond pad burnishing head. The term "70%" describes the size of the burnishing head and is understood by those skilled in the art. The term "4.5 mil" refers to the width of the channels 12 between diamond pads 4. The vertical axis is the average hit voltage determined by a glider head. (A glider head is a test head used to test a disk for the presence of asperities and voids on the disk surface. A glider head provides an output "hit voltage" indicative of the size of the asperity or void encountered.) The horizontal axis is the test radii of the disks tested. The line with diamond data points is the average hit voltages of five disks before burnishing. The line with square data points represents the average hit voltage of the same five disks after two passes with diamond pad burnishing head. FIG. 3B is a graph similarly depicting the performance of the same burnishing head after eight hours of continuous use. FIG. 3B also depicts the initial average hit voltages of five unburnished disk and the average hit voltages on the same disks after two passes with the used diamond pad burnishing head. The used diamond pad burnishing head damaged the disks at the radii 1340 and 740 as illustrated by the 2-pass data line having a higher hit voltage than the initial data line.
As shown in FIG. 1, burnishing head 2 is asymmetrical. Diamond pads 4 are intended to travel over the surface of disk 14 in a specific direction, such that any protrusions on the surface of disk 14 meet cutting edges 6 and 8 of diamond pads 4 at the greatest oblique angle possible. In other words, each protrusion should be sliced from one side to the other by cutting edge 6 or 8, rather than confronted all at once by cutting edge 6 or 8. Tapered edge 10 further limits the direction of travel of burnishing head 2 relative to disk 14 because tapered edge 10 is the leading edge as illustrated in FIG. 2.
FIGS. 4A and 4B illustrate the alignment of prior art burnishing heads 2A and 2B when mounted to a suspension arm 13 over disk 14 rotating in the direction of arrow 18. FIG. 4A shows burnishing head 2A mounted to suspension arm 13 such that burnishing head 2A is in a transverse direction relative to suspension arm 13. Thus, burnishing head 2A is known as a "transverse" burnishing head. FIG. 4B shows burnishing head 2B mounted to suspension arm 13 such that burnishing head 2B is in line with suspension arm 13. Thus, burnishing head 2B is known as an "in-line" burnishing head. The way in which burnishing heads 2A or 2B are mounted to suspension arm 13 depends on the alignment of diamond pads 4 (in phantom lines in FIGS. 4A and 4B) and which edge is the tapered leading edge 10 (FIG. 1). As discussed above, cutting edges 6 and 8 of diamond pads 4 are more efficient if they meet asperities 20 at the greatest angle possible. If burnishing heads 2A and 2B are incorrectly mounted to suspension arm 13, cutting edges 6 and 8 will not contact asperities 20 at the desired angle. Thus, care is required during manufacturing so that diamond pads 4 are positioned correctly on burnishing heads 2A and 2B and also in the mounting of burnishing heads 2A and 2B to suspension arm 13 so that burnishing heads 2A and 2B are facing the correct direction relative to suspension arm 13. Accordingly, a universal burnishing head is needed that eliminates the need to determine whether the head is a transverse or in-line burnishing head and which edge is the leading edge.